(110d) Graphene Supported Bifunctional Catalysts for Oxygen Electrodes In Rechargeable Lithium-Air Batteries

Rechargeable lithium-air batteries offer great promise for transportation applications due to their high specific energy and energy density compared to all other battery chemistries.  Therefore such batteries could be developed for powering electric vehicles, enabling driving ranges comparable to gasoline powered automobiles. Although the theoretical discharge capacity of Li-Air cell is extremely high, the practical capacity is much lower and is always cathode limited.  On charging, the cathode acts catalytically to evolve oxygen (the oxygen evolution reaction, OER) and on discharge acts to reduce oxygen (the oxygen reduction reaction, ORR).  However, due to the slow kinetics and higher overpotential especially in OER together with clogging of Li₂O₂ in the pores of air electrode limit the re chargeability of Li-Air batteries.  A key for rechargeable systems is the development of an air electrode with bifunctional catalyst on an electrochemically stable carbon matrix. The use of Graphene as a stable catalyst matrix for Air cathode has been studied in this work.  A Li-Air cell constructed using an air cathode consists of nano Pt on graphene nanosheets (GNS) has showed promising improvement of 85% energy efficiency with average capacity of 1800 mAh/g and more than 30 cycles without significant capacity fading.  Replacement of Pt with nano structured bifunctional catalysts of the general formula La_1-xA_xCo_1-yB_y (A = Ca, Ce; B= Mn, Fe, Ni, Cu) is under investigation.  The effects of microstructure and loading of several GNS (with different sizes and number of layers) on the pore size distribution pore volume and surface area, as well as the relationship of particle size and the synthesis route of catalyst to the electrochemical performance will be discussed.  These developments will help to exceed the specific energies of 1000 Wh/kg for practical purposes.